Australian Natural Resources Atlas

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Rangelands - Overview

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Location map of Tiwi Coburg bioregionphotograph

Tiwi Coburg

Summary

ATSIC Boundaries

Catchment Basins

Statistical Local Areas

Introduction

This bioregion covers an area of 9,900 sq kms. It includes the Tiwi Islands (Bathurst and Melville Islands), Cobourg Peninsula and Croker Island. The main population centres in the bioregion include Milikapiti and Pularumpi (Melville Island), Nguiu (Bathurst Island) and Minjilang (Croker Island). Bathurst and Meville Islands have a population of 2,150.

For more information on this region refer to the Darwin-Kakadu, and Arnhem Land regions in the Tropical Savanna Co-operative Research Centre web site: www.savanna.ntu.edu.au/information/r0/t0/r0_t0.html

Natural Environment

Climate

The region is within the tropical monsoonal north of Australia, with a distinct wet dry season and high temperatures throughout the year. The region's climate is influenced by its location on the coast with rainfall being higher than the adjacent inland regions. This bioregion has the highest rainfall in the Northern Territory.

The mean annual rainfall ranges between 1600mm and 2060mm with 90% of rain falls between November and March (Kerle, 1996). Mean temperatures are fairly consistent throughout the region, with the highest temperatures being in the build up to the wet season in November. Milikapiti has a temperature range of 18°C-31.2°C in the winter and 23.7°C-32°C in summer.

Climate averages are available for Milikapiti (Melville Island) and Cape Don (Cobourg Peninsula):

http://www.bom.gov.au/climate/map/climate_avgs/a14ga.shtml

Temperature and rainfall graphs are available for Darwin (closest weather station):

www.bom.gov.au/climate/forms/map_forms/new_imagemaps/nt_name.html

Current seasonal conditions and their historical context can be provided by satellite imagery. The Normalised Difference Vegetation Index (NDVI) is a measure of the vegetation 'greenness'. The NDVI for the Tiwi Cobourg bioregion for this year and previous years can be found at: http://www.environment.gov.au/erin/ndvi/ttrace/tiw.html

Landforms and hydrology

The Coburg Peninsular and Tiwi Islands consist of gently sloping terrain of Cretaceous (65-141 million year old) lateratised sandstones and siltstones sediments of the Money Shoal Basin. The bioregion is characterised by plains and coastal dunes. The bioregion has no major river systems.

For more detailed geological information and map refer to the Australian Geological Survey Organisation website: www.agso.gov.au/map/ and the Northern Territory Geological Survey website: www.dme.nt.gov.au/ntgs/ntgs/geo_overview/geo_over.html

Gurig National Park within this bioregion is a wetland of international importance listed by the Ramsar convention. The area covers almost all of Cobourg Peninsula including an extensive intertidal area. The peninsula has many extensive tidal flats, estuaries, riverine wetlands and melaleuca swamps. For more information about the site refer to: http://www.biodiversity.environment.gov.au/environm/wetlands/ramsar/siteindx.htm.

Soils

The soils range from sandy red and yellow earths or podsols with some siliceous sands and heavy alluvial soils and clays associated with the floodplains. (Thackway &Cresswell, 1995, Kerle, 1996).

For more soils information refer to the Digital Atlas of Australian Soils

Vegetation

There has been no inventory of plant species in this bioregion, although some information is presented by Connors et al (1996) as part of the broader Top End Coastal bioregion www.nt.gov.au/paw/fauna/bau/intro.htm

The predominant vegetation communities are eucalypt forest and woodlands with tussock and hummock grass understorey (Connor et. al., 1996). However there is a diversity of vegetation communities in the bioregion, varying with topography and drainage (Kerle, 1996). These are:

Monsoon vine forest thicket

This bioregion has relatively large areas of coastal, spring and riparian monsoon rainforests, which typically occur as small species-rich patches

Undulating low plateaux, and gravel rises

The most extensive vegetation type away from the immediate coast is eucalypt forest co dominated by darwin stringybark (Eucalyptus tetrodonta) and darwin woolly butt (E. miniata), often in association with melville island bloodwood (E. nesophila), ironwood (Erythrophleum chorostachys) and northern cypress pine (Callitris intratropica). Many forests also have a well developed shrub layer including Acacias, fan palm (Livistona humilis), the tall palm (Gronophyllum ramsayi), cycads and screw palm (Pandanus spiralis).

Eucalypt woodlands occur in more restricted areas, typically on heavier soils. The dominant species include Corymbia latifolia and C. oligantha.

Riverine and poorly drained soils

Paper bark swamps occur on some creek systems and drainage depressions. Species include Melaleuca leucadendra, M. cajuputi and M. viridiflora). Grasslands and sedgelands occur on the seasonal floodplains including wild rice (Oryza rufopogon), and spikerush (Eleocharis spp.).

Coastal communities

Coastal communities vary from beach dunes to salt flats, heathlands, swamps, shrublands and mangrove closed forest. There are a number of species of mangrove, the most common being the white mangrove (Avicennia marina). Dunes may include coastal sheoak (Casuarina equisetifolia).

Fauna

There has been no inventory of animal species in this bioregion, although some information is presented by Connors et al (1996) as part of the broader Top End Coastal bioregion (refer to:

www.nt.gov.au/paw/fauna/bau/intro.htm).

Threatened species known from this bioregion include butler's dunnart (Sminthopsis butleri), false water-rat (Xeromys myoides) and red goshawk (Erythrotriorchis radiatus), and a number of subspecies of birds and mammals have been described as being endemic to the Tiwi Islands.

Land Tenure & Use

Land tenure

The bioregion consists of Aboriginal freehold land and nature reserves. Some of the land reserved for conservation is also Aboriginal land, which is on lease as national park, including parts of Gurig National Park (Cobourg Peninsula). The Cobourg Marine Park includes the small islands south of Cobourg Peninsula.

Land use

Tourism has become an important industry in the region, both to the Tiwi Islands and Gurig National Park. Forestry has been a significant industry on the Tiwi Islands, and there are ongoing proposals for further expansion. Pearl-farming and other aquaculture industries are commercially significant.

Condition Of The Landscape

Land degradation

This bioregion is generally in good condition.

Feral animals, particularly water buffalo, have affected some environments. Pigs, buffalo and cattle are causing widespread damage to monsoon rainforest patches. Changes in fire regime have also led to degradation of monsoon forests, and are likely to have impacted on the floristic and structure of Eucalypt forests. (Woinarski, et al., in prep.).

Tourism is having localised impacts, including the impact of 4 wheel drive vehicles.

Pest species

The isolation of most of this bioregion has offered reasonable protection against weeds, although there are localised outbreaks of some weed species, most notably including mission grass (Pennisetum polystachion) and mimosa (Mimosa pigra). The introduced pasture species para grass (Urochloa mutica) is widespread on Croker Island and there are a number of areas of infestation on mainland sites.

There are high densities of some feral animals, most notably of pigs (Sus scrofa) on Bathurst Island and Cobourg Peninsula, buffalo (Bubalus bubalis) and horses (Equus caballus) on Melville Island and banteng (Bos javanicus) on Cobourg Peninsula.

Social & Economic Aspects

People

Bathurst and Melville Islands are Tiwi Aboriginal land and Croker Island is part of Arnhem Land. Transport to the communities within Arnhem Land and the Tiwi Islands is generally by air, although transport of goods to many of the coastal Aboriginal settlements is by barge, and limited road access is possible to some areas in the dry season.

Aboriginal people have occupied the north coast of the Northern Territory for at least 60,000 years, utilising resources from the land and sea, and until early this century trading with visitors from the islands to the north, the Macassans. Many Aboriginal people still live in communities within the region and maintain traditions.

The bioregion is within the ATSIC regions of Darwin and Jabiru are managed by the Yilli Rreung and Jabiru regional councils respectively (McLennan, 1997). The Tiwi Islands are administered by the Tiwi Land Council, while Cobourg Peninsula and Croker Island fall within the jurisdiction of the Northern Land Council. For more information on the Aboriginal people of this region refer to Horton, (1994) and the relevant websites in the reference list.

Resources, References & Contacts

Publications

Connors G., Oliver B., & Woinarski, J. 1996, Bioregions in the Northern Territory: Conservation Values, Reservations Status and Information Gaps. Final report to ANCA National Reserves System Cooperative Program (Project N607), Parks and Wildlife Commission of the Northern Territory, Palmerston, Northern Territory. (www.nt.gov.au/paw/fauna/bau/intro.htm.)

Hema Maps 1997, Australia Touring Atlas, Fergies Colour Printers, Brisbane, Queensland.

Horton, D. R. 1994, The Encyclopaedia of Aboriginal Australia, Aboriginal Studies Press for the Australian Institute of Aboriginal and Torres Strait Islander Studies, Canberra, ACT.

Kerle, J.A. 1996, Bioregions of the Northern Territory. Draft report Conservation Commission of Northern Territory, Palmerston, Northern Territory.

McLennan. W. 1997, 1994 National Aboriginal and Torres Strait Islander Survey: Social Atlas, Australian Bureau of Statistics, Canberra, ACT.

Thackway, R. & Cresswell I.D. 1995, An Interim Biogeographical Regionalisation for Australia: a Framework for Setting Priorities in the National Reserves System Cooperative Program, Australian Nature Conservation Agency, Canberra.

Woinarski J., Fensham, R., Whitehead, P. & Fisher, A., with map production by Verhagen, C. in prep., Biodiversity in the Australian Rangelands: a Review of Changes in Status and Threatening Processes. Draft report prepared as a resource document for Project 3: Developing an Adaptive Framework for Monitoring Biodiversity in Australia's Rangelands, of the National Land and Water Resources Audit, Theme 4 (Rangelands monitoring) by the Tropical Savannas Cooperative Research Centre, Darwin, Northern Territory.

Websites and contacts

Aboriginal languages of Australia

http://www.dnathan.com/VL/

Aboriginal Studies WWW Virtual Library

http://www.ciolek.com/WWWVL-Aboriginal.html

Australian Torres Strait Islanders Commission (ATSIC)

www.atsic.gov.au

Australian Geological Survey Organisation, Geology of Australia

www.agso.gov.au/map/

Bureau of Meteorology, Climate averages

http://www.bom.gov.au/climate/map/climate_avgs/a14ga.shtml

http://www.bom.gov.au/climate/map/climate_avgs/a14f.shtml

Bureau of Meteorology, Temperature and Rainfall graphs

www.bom.gov.au/climate/forms/map_forms/new_imagemaps/nt_name.html

Bureau of Rural Sciences, Digital Atlas of Australian Soils

www.affa.gov.au/content/output.cfm?ObjectID=D2C48F86-BA1A-11A1-A2200060B0A05758

Charles Sturt University: Guide to Australia – NT

http://www.csu.edu.au/australia/nt.html

Connors G., Oliver B., & Woinarski, J. 1996, Bioregions in the Northern Territory: Conservation Values, Reservations Status and Information Gaps. Final report to ANCA National Reserves System Cooperative Program (Project N607), Parks and Wildlife Commission of the Northern Territory, Palmerston, Northern Territory. (www.nt.gov.au/paw/fauna/bau/intro.htm.)

Department of Primary Industries and Fisheries, Rangelands of the Northern Territory

www.nt.gov.au/dpif/rangelands/rl_index.shtml

Department of the Environment and Heritage, Normalized Difference Vegetation Index information including bioregional information

www.environment.gov.au/erin/ndvi/index.html

Northern Land Council

www.nlc.org.au

Northern Territory Department of Lands, Planning and Environment

www.lpe.nt.gov.au

Northern Territory Geological Survey

www.dme.nt.gov.au/ntgs/ntgs/geo_overview/geo_over.html

Northern Territory Government Tourism www.nt.gov.au/ntg_internet/profile/regions_alice_springs.shtml

and

nttc.com.au/

Tropical Savanna Co-operative Research Centre

www.savanna.ntu.edu.au/information/savannaexplorer.html

Link to the Map Maker to make a map using this information.

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